Couplings are known which enable two coaxial components to rotate together. In one such coupling, one of the components is provided with a spigot which locates in a recess formed in the other component to which it is to be joined. The spigot cooperates with the recess producing an interference fit which maintains the two components in alignment so they rotate coaxially. A problem with such a coupling is that the spigot and recess have to be machined within fine tolerances to produce an interference fit and maintain the two components in alignment. The manufacturing process to produce a coupling within the required tolerances is both time consuming and expensive.
With a coupling of this type, alignment problems may arise between the two components if the spigot and recess experience differential expansion. This may be as a result of the two components having different coefficients of thermal expansion or if one of the components experiences a different temperature to the other component. The interference fit loosens and misalignment occurs resulting in eccentric rotation of the components. The eccentric rotation of the components may result in vibration between the radial faces and produce uneven wear on these faces.